The present invention relates generally to calibration and remapping methods for reducing the distortions in an image obtained by a scanning beam device. More specifically, the present invention relates to image remapping and drive remapping methods that reduce distortions caused by positional uncertainties of a scanning element during a scan pattern.
One promising type of scanning beam device is a scanning fiber device. In a scanning fiber device, light is projected out of an end of a single, cantilevered optical fiber. The optical fiber is vibrated and scanned in one or two dimensions in a scan pattern so as to scan an illumination spot through an optional lens system and over a target area. Theoretically, knowing the drive signal that creates the scan pattern of the illumination spot allows a controller to know the exact position of the illumination spot throughout the scan pattern. Consequently, that allows for construction of an image on a pixel by pixel basis. If the scanning fiber device is used to form an image, the light projected out of the end of the optical fiber is modulated during the scan pattern depending on the pixel position so as to form a desired image on the target area. To acquire an image of the target area, the illumination spot is scanned over the target area in the scan pattern and the backscattered light is captured by a photosensor in time series. Because the motion of the fiber is predictable, the sensed light can be correlated with the time position of the capture of the illumination spot on the target area and a two-dimensional image of the target area can be created one pixel at a time. Some exemplary scanning fiber device are described in U.S. Pat. No. 6,294,775 B1 (Seibel) and U.S. Pat. No. 6,563,105 B2 (Seibel) and U.S. Patent Application Publication Nos. 2001/0055462 A1 (Seibel) and 2002/0064341 A1 (Seibel), the complete disclosures of which are incorporated herein by reference.
However, in order to properly construct the image on a pixel-by-pixel basis, the precise positional information of the scanning element, such as the optical fiber should be known by a controller for each and every point in time of the scan pattern. Any positional inaccuracy (e.g., the illumination spot position is not where it should be) will result in a distortion in the image. Theoretically, knowing the drive signal that is used to scan the optical fiber should allow the controller to know the exact position of the illumination spot at each and every point during the scan pattern. In practice, however, environmental variables and manufacturing variables, such as non linear drive electronic, non-linear drive mechanisms, aberrations in an imaging system of the fiber scanning system, the sensitivity of the scanning fiber device around the resonant frequency, and other factors, add to the positional inaccuracy of the illumination spot during the scan pattern and will add distortion to the image constructed by the scanning fiber device.
While the optical fiber may be scanned at any frequency, in most embodiments, the drive signal is chosen to substantially match the resonant frequency of the optical fiber, since scanning at the resonant frequency provides the desired radial displacements with a minimal use of energy. Scanning at the resonant frequency, however, puts the illumination spot exactly 180 degrees out of phase with the drive signal. Consequently, the optical fiber is sensitive to frequency changes immediately around the resonant frequency. For example, if the drive signal is not exactly at resonant frequency, the illumination spot moves from 180 degrees out of phase and moves closer to being in-phase with the drive signal, which further adds distortions into the image.
Consequently, what are needed are methods, systems, software, and kits which can reduce image distortion in an image created or acquired by a scanning beam device, such as the scanning fiber device.